First Cycle Analysis And Modification Study On Nmc Cathode Material For Lithium Ion Batteries

With the energy density requirements getting higher and higher,further improving the energy density of lithium-ion battery has been a hotspot.However,the problem of irreversible capacity of materials,as well as cycle performance and rate capability at high cutoff potential,remains to be solved.In this paper,LiNi0.5Mn0.3Co0.2O2 was chosen as the object of study,and the reason of the irreversible capacity loss of the NMC material during the cycle was analyzed.The effect of surface coating on the Coulombic efficiency and electrochemical properties of the material under high voltage were investigated.The main contents are as follows:1.The analysis of the charge/discharge process,the surface and structure of the material shows that the irreversible capacity of the first cycle comes from two aspects:the side reaction and the dynamics factors during charge and discharge process at high potential;2.In-situ XRD characterization was used to further analyze the irreversible structural changes of the initial charge-discharge process.The capacity loss analysis of the material under different lithium-off conditions at low potential showed that the capacity loss caused by the structural and kinetic factors of the material itself accounts for more than 60%of the total irreversible capacity,the impact of electrolyte side effects is mainly reflected in the high potential(>4.3 V).3.The effect of coating modification on the electrochemical properties of the material under high voltage was studied.(LiBO2)was coated on the surface of LiNi0.5Mn0.3Co0.2O2 by liquid-phase coating.The results showed that the electrochemical performance could be enhanced obviously when the coating amount is 2wt%.After 50 cycle,the discharge specific capacity is 171.2 mAh g-1 in the voltage range of 3.0 V-4.5 V with the capacity retention rate was 91.23%while the capacity retention rate of bare was only 53.19%.The rate test showed that the specific capacity of the 2wt%coating material reached 114.7 mAh g-1 at 1OC rate which was almost two times of bare sample.Thermal test showed that the LiBO2 coated material was better than that of unmodified one.4.The electrochemical performance of the composites was improved by Al2O3 and rock salt LiTiO2 coating.The Al2O3 coating improved the cycle performance effectively with the capacity retention of 90.23%at 0.2C current after 50 cycles,however,the improvement of the rate capability was not obvious.After LiTiO2 coating,the efficiency of the initial Coulombic efficiency increased to 86.90%,nearly 5%higher than the uncoated material.